A woman has been charged with posing as a medic and injecting drugs into a spectator at the prestigious Blenheim Palace International Horse Trials.
Cassandra Grant, 38, of Bristol, allegedly pretended she was a nurse and administered drugs to people attending the three-day event in Oxfordshire earlier this month.
She had been volunteering at the event when it is alleged she approached the medical tent and claimed she was a nurse.
On Friday she appeared at Oxford Magistrates' Court charged with causing actual bodily harm and fraud by false representation after administering an injection of an anti-sickness drug to a person seeking first aid at the Blenheim Horse Trials.
Following the event, Blenheim Palace's chief medical officer Sue Smith alerted police.
Event organisers said in a statement: "The safety of everyone who attends Blenheim Palace International Horse Trials is our highest priority.
"We are investigating what access this person might have had to people who came into our first aid facilities.
"As soon as we were made aware that someone may have been trying to impersonate a medical professional we referred this to the police and we are therefore not able to comment further."
Magistrates have transferred her case to Oxford Crown Court to be heard next month.
A Thames Valley Police spokesman said: "The charge of fraud by false representation is in connection with an allegation that Grant falsely claimed to be a medical professional at Blenheim Horse Trials earlier this month.
"The assault is in relation to an allegation that Grant gave a patient an intravenous injection of an anti-sickness drug at the horse trials."
The show uses more than 600 volunteers for a variety of roles available including fence judges, crossing point stewards, site assistants and grandstand stewards.